As discussed in the referenced and incorporated disclosure, the use of therapeutic gases to treat a human or animal patient has been known in the art for many years. A number of different gases may be added to a respiratory gas that is inhaled by a patient. It is noted that this application merely refers to a “patient” because it is intended to encompass within its scope the is following situations: a spontaneously breathing, non-ventilated patient, as well as a spontaneously breathing, mechanically-ventilated patient, as well as a non-spontaneously breathing, mechanically-ventilated patient. Accordingly, the term “patient” is intended to cover all of these situations and/or combinations thereof. These gases may be used to achieve some therapeutic effect, service a diagnostic function or have some other desirable purpose. Such gases will be referred to herein as therapeutic gases. One skilled in the delivery of therapeutic gas will understand that the disclosure can be used to teach either human or animal patients. Accordingly, no limitation to human is intended by references to patient in this disclosure.
One therapeutic gas is nitric oxide (NO), which is administered by inhalation in low concentrations to treat primary or secondary pulmonary hypertension or other diseases. In many cases, nitric oxide or other therapeutic gases come from a high concentration source such as a high concentration compressed gas cylinder. The gas source may be pure or may contain some concentration of therapeutic gas in a carrier gas. There may also be cases where more than one therapeutic gas is used, with or without a carrier gas or gases. It is often necessary to dilute therapeutic gas to a lower concentration and mix it with air and/or oxygen prior to delivery to the patient. This dilution may be necessary to achieve a desired dosage concentration and/or to avoid or reduce adverse bioeffects that may occur if high concentration gas is delivered to the patient. If the therapeutic/carrier gas is not sufficiently oxygenated, it is necessary to mix it with air prior to delivery to the patient. In some cases, it is necessary to add supplemental oxygen to the mixture to avoid a hypoxic respiratory mixture or to enrich the oxygen content of the respiratory gas above twenty-one percent. In the latter case, the oxygen will also be considered as a therapeutic gas.
NO is one of a number of therapeutic gases that are administered to a patient and require dilution from a high concentration form to a lower, safer concentration before administration to a patient. NO will be the primary focus of this disclosure; however, one skilled in the surgical arts will understand that the disclosure can be used to teach other gases as well. Accordingly, no limitation to NO is intended by the references to NO in this description.
The art contains several devices and systems to deliver therapeutic gas to a patient.
The referenced disclosure discusses several systems for administering therapeutic gas to a patient.
Many systems that are used to administer therapeutic gas to a patient include primary gas sources in the form of pressurized cylinders. Some of these systems include a flow direction check valve downstream of the inlet to seal the downstream portions of the system when the supply pressure is removed. However, a check valve isolation system may have drawbacks if used in certain circumstances.
When a pressurized gas source is exchanged, there exists the possibility that air will be trapped within the inlet volume of the system plumbing that is exposed to air during the source exchange. Specifically, in a check valve system, this volume includes the volume upstream of the sealing mechanism of the check valve. It is desirable to keep that exposed volume of plumbing as small as possible so the resulting trapped air volume is reduced. Any trapped air will normally degrade the quality of the high purity gases contained within the remainder of the system when intervening valves are opened. This degradation is proportional to the volume of trapped air.
Therefore, it is desirable to maintain this dead volume to a minimum. Note that the concept of dead volume should also be read to include dead surface area within the scope of this discussion. The trapped air volume will also be referred to as the dead volume in this disclosure. Surface area plays an important role in gas plumbing quality since contaminants often preferentially adhere to surfaces and can be extremely difficult to remove.
Furthermore, it is advantageous to provide a system sealing action as close to the supply inlet as possible to further minimize the dead space volume upstream of the sealing surfaces.
Typically, a flow direction check valve is not able to achieve all of these goals.
It is noted that it is possible to flush or purge the system to remove contaminated gas from dead space regions. However, for purging to be effective, the dead space must be substantially swept out and internal surfaces scrubbed by periods of high gas flow. If there are poorly swept regions within the dead space, purging will have to be extended to allow for diffusion and other gas exchange mechanisms to remove or dilute the contamination. Therefore, there is a need for a means for ensuring proper purging of a system used to administer therapeutic gas to a patient.
Furthermore, purging requirements are strongly dependent on the relative size and geometry of the contaminated volumes and surfaces. Purging is often complicated in many situations due to possible toxic effects of the therapeutic gases on bystanders and the high cost of medical grade gases.
The incorporated disclosure notes that there is a further need for a valve that will make purging most efficient and effective.
Furthermore, the referenced disclosure notes that an autonomous gas delivery system should be able to detect the supply pressure so when a pressurized cylinder has been attached and the supply valve opened, a control system is signaled.
The referenced disclosure further notes that in order to maintain low inlet dead space, a supply pressure sensor must be located on the downstream side of an inlet sealing mechanism. In the prior art, a simple back flow prevention check valve has provided this function. A check valve will seal when there is a lower supply pressure on the upstream side of the check valve than in the downstream plumbing (thus checking the backward flow of gas). If the check valve seals, the pressure sensor, which is located further downstream in the system than the check valve, will continue to show the last supply pressure when the check valve closes. The pressure sensor may not indicate the actual supply pressure, which typically drops to atmospheric pressure when the supply is disconnected. If, subsequent to this, a supply is attached that is at a lower pressure than the checked pressure, the system will not be able to detect the connection until the pressure downstream of the check valve has been bled off as well as not at all.
Accordingly, as discussed in the referenced disclosure, there is a need for a means for sealing a system such as disclosed herein which will be able to fully detect pressure and control the flow of the system during changing of gas sources.
The referenced disclosure observes that in general, it is desirable to close off the inlet of a system such as disclosed herein when a supply is detached and to maintain the inside of the high purity system at a slight positive pressure with respect to atmospheric pressure.
The advantages of this isolated input but slight remaining positive pressure situation include: the chance of contamination is reduced; minor leaks that may be present will tend to leak in an outward fashion; the limited maximum internal to inlet side pressure allows the downstream pressure sensor to detect a disconnection of a supply with any significant pressure; and allows the system to detect the connection of another supply with a pressure significantly above atmospheric.
As discussed in the referenced disclosure, there is a need for a means for connecting the system of the present invention to a source of gas that will reduce the possibility of contamination of the system. Therefore, there is a need for a mechanism that can minimize dead space volume.
The referenced disclosure discusses an equalizing valve that simultaneously satisfies a number of objectives and overcomes many problems associated with prior therapeutic gas delivery systems.
Still further, there are situations in which the main supply source for a system must be removed from the system. For example, the main source must often be removed to be replaced with an alternate source. Replacement may be required if: the primary source is depleted; if a portable gas source is being replaced by a stationary source (or vise versa); or if the gas source is being exchanged for an alternate therapeutic gas composition. Other situations that may require the removal of the gas source include but are not limited to preparation for temporary storage or shipment, periodic maintenance and transport between use locations.
As discussed in the referenced disclosure, contamination of the therapeutic gases, such as mixing therein atmospheric gases, is undesirable.
In many therapeutic gas delivery situations, gas delivery to the patient must be temporarily disrupted in order to change supply source, or the like. Such disruption is undesirable. In order to obviate such disruption, some gas delivery systems include either a second large source or an external back-up source of therapeutic gas. Either of these solutions can be costly and cumbersome.
Still further, if, for some reason, the primary gas source ceases supplying gas to the system and an operator does not immediately replace the gas source, delivery of gas to the patient may be interrupted, or even contaminated. Neither of these situations is desirable.
Therefore, there is a need for a therapeutic gas delivery system in which continuous gas delivery to a patient is ensured, even if the main gas source ceases delivering gas for a short period of time.